1. Field of the Invention
The present invention relates to an improved system and method for manufacturing laminated structures. More specifically, the present invention relates to an improved system and method for minimizing initial alignment error in printed circuit board (PCB) manufacturing.
2. Description of the Related Art
The related art involves a process for producing printed electronic circuits, including multilayer circuits by endothermic induction heading as discussed in PCT/IT2003/000403 by Ceraso, et al., (published as WO 2004/103042) [the Ceraso system] the entire contents of which are herein incorporated by reference.
In the Ceraso process and system, plastic laminates with copper laminae for electronic circuits are provided including multilayer circuits, a cold press secures an endothermic heating pile of a plurality of packages. During processing, a ferromagnetic core having an alternating current winding is positioned proximate the endothermic heating pile and induces an inductive field within the copper laminae to warm the heating pile (which includes resin sheets (also known commonly as “pre-preg”)), and laminate the individual layers together.
The solution created by this reference eliminates several of the detriments known in the related-art heating techniques for rapidly forming multilayer laminates, and has been widely adopted by the industry as a result. Unfortunately, the Ceraso process, while more rapid, fails to enhance accuracy and commonly incurs higher quality control loses.
Thus, while the present discussion incorporates filly the entire detailed disclosure of this reference nothing herein shall prevent the systems and devices discussed herein from employing the alternative forms of laminate heating and sealing discussed within the Ceraso reference, as noted above noted above.
A. Tooling Alignment Systems
The related art involves the use of different types of alignment systems each offering advantages and disadvantages. Presently these differing types include “pin-based” and “riveted-type” registration systems in laminated structure manufacturing. While each system succeeds in fixing multiple laminated structures relative to each other, each system also provides an unacceptable alignment tolerance level addressed by the present invention.
There are many tolerances associated with the production of a circuit board. Unfortunately, these combined errors or “tolerance errors” build up throughout the course of lamination imaging and lamination tooling and ultimately have an exponential impact on alignment accuracy. With the increasing reduction in dimensional circuit design these tolerance errors are unacceptable. We will examine the punched or drilled hole tolerances below, at different stages of the manufacturing process.
The tolerance or alignment errors resulting from conventional alignment systems are also revealed through the process of imaging inner layers of an assembled block of laminated members. Imaging inner layers reveals internal alignment errors.
When imaging inner layers, imaging for front-to-back is typically performed using two methods, (i) pinning the artwork to holes on the inner layer or (ii) roughly imaging the circuit pattern to the edges of the inner layer (so called edge-imaging).
In the first method, the conventional tooling holes that were used to image the circuit pattern on the inner layer are also used to align the layers to each other in lamination. The downside to this method is that typically the same holes are used; and consequently, any distortion relative to these holes will have a negative affect as the inner layer is processed throughout the remainder of the lamination process. This problem is greatly affected during lay-up and as the layer thickness is reduced.
In the second method (edge imaging), the hole tolerance for imaging has been eliminated, and this is much more accurate as camera assisted imaging is now possible. The newer exposure machines can now align the front and back artwork via a CCD camera positioning system, by doing so they minimize the tolerances of the punches holes in the artwork as well as in the innerlayers. Unfortunately, this edge imaging method still requires the use of holes for ultimate alignment of a completed lamination and hence still incurs alignment error.
A conventional manufacturing step involves attempting to align the layers prior to lamination. This step in the manufacturing process is conventionally accomplished by many different methods; the most common methods in use today are pin lamination, riveting, and pin bonding.
In “pin Lamination,” systems the most common tooling pattern is the 4-slot centerline tooling. The main advantage of this tooling scheme is that it allows for easier lay-up than lay-up on four round holes. The slots compensate any material movement in the etching process (allowing and encouraging X-Y shifting), whereas the use of simply four round holes would cause distortion on the inner layer when pinned to four-fixed pin in a lamination plate (four round hoes prevents shifting between layers causing gapping, and ultimately layer shifting. So if the slots are used it is conventionally easier to lay-up and buckling is similarly minimized, but there are many tolerances error associated with this process. Unfortunately, these tolerances exist regardless of the numbers of cameras used on a post-etch punch process.
Referring now to FIG. 1, in reviewing the impact of punch and slot alignment systems, the multiple error-sources are noted on Table 1 (FIG. 1) along with the associated error ranges. In reviewing FIG. 1 (Table 1), it should be noted that even under the best conditions, layer-to-layer registration capability with pin lamination is at best approximately 50-75 microns (um).
Finally, as a further disadvantage in the conventional alignment arts, pin lamination is not flexible when changing panel sizes, shifting between panel sizes for custom lamination sets, etc. When changing panel sizes, a customer needs to purchase different lamination and separator plates for each panel size to be processed, and this is extremely expensive.
Referring now to FIG. 2 (Table 2), in conventional “riveting systems,” the main advantage of this tooling scheme is that it allows for more flexibility in selection of panel sizes than pin lamination (because rivet holes may be positioned as needed). Unfortunately, this process also has many of the same detrimental tolerance issues.
These detrimental tolerance issues include the need to line-up holes target locations prior to riveting, the need to punch or drill the holes, and ultimately after hole-creation the layers must be placed on pins prior to riveting to maintain alignment during the riveting process. In sum, the conventional riveting system tooling hole tolerances are the same as in pin lamination, but there are also the following tolerances associated with riveting. These tolerances are summarized generally in FIG. 2.
As noted in FIG. 2, the layer shift due to rivet distortion itself is a mechanical error that is very difficult to overcome, thus making the riveting generally a process for low layer count and low-density boards.
Finally, in conventional “pin bonding systems,” much like riveting, the main advantage of this tooling scheme is that it allows for more flexibility in choosing panel sizes than in the above-discussed pin lamination systems. Unfortunately, pin bonding systems also possess some of the same tolerances.
The tolerance issues in pin bonding systems include that the line-up holes prior to bonding must be punched or drilled, and that the layers must be physically or mechanically placed on pins prior to bonding for the alignment. These tooling hole tolerances and the positioning tolerances are the same as in pin lamination.
Ultimately, after conventional alignment systems the bonding process, whether accomplished by hot heads, ultrasonic or inductive is essentially the same. During initial bonding, the so called pre-preg (resin sheets) at certain points, typically at six points on the long edge of the panel, is heated so that the resin forms a bond point between sheets. During this conventional bonding process, the results from pin bonding are usually better than pin lamination; and this is because the lay-up is performed on the same template for a certain panel size. This is because in conventional pin lamination the lay-up is on long pins and on different lamination plates that have different tolerances from pin to pin.
Of the different methods discussed, the pin bonding is the most flexible, this eliminates the costly tooled lamination and separator plates, the copper foil does not need to be punched, and there are no consumables required, such as lamination pins or rivets.
Ultimately, what is not appreciated by the prior art is: (a) the need for a highly accurate and repeatable circuit board laminate registration system that is flexible, particularly one that does not magnify error in a multi-layer set-up, but remains instead within a predictable and calculable tolerance range; (b) the need for a repeatable alignment system and structure that enables induced heating for multi-layer systems; (c) the need for a pre-alignment and imaging station for determining a pre-assembly assignment position; and (d) the need for an in-situ pin-less-alignment system.
Accordingly, there is a need for an improved system and method for manufacturing laminated structures that responds to the needs noted above.